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diff --git a/src/mongo/s/balancer/balancer_chunk_selection_policy.h b/src/mongo/s/balancer/balancer_chunk_selection_policy.h
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+/**
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <boost/optional.hpp>
+#include <vector>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/s/balancer/balancer_policy.h"
+#include "mongo/s/catalog/type_chunk.h"
+#include "mongo/s/chunk_version.h"
+
+namespace mongo {
+
+class ChunkType;
+class NamespaceString;
+class OperationContext;
+template <typename T>
+class StatusWith;
+
+/**
+ * Interface used by the balancer for selecting chunks, which need to be moved around in order for
+ * the sharded cluster to be balanced. It is up to the implementation to decide what exactly
+ * 'balanced' means.
+ */
+class BalancerChunkSelectionPolicy {
+    MONGO_DISALLOW_COPYING(BalancerChunkSelectionPolicy);
+
+public:
+    /**
+     * Describes a chunk which needs to be split, because it violates the balancer policy.
+     */
+    struct SplitInfo {
+        SplitInfo(ShardId shardId,
+                  NamespaceString nss,
+                  ChunkVersion collectionVersion,
+                  ChunkVersion chunkVersion,
+                  const BSONObj& minKey,
+                  const BSONObj& maxKey,
+                  std::vector<BSONObj> splitKeys);
+
+        std::string toString() const;
+
+        ShardId shardId;
+        NamespaceString nss;
+        ChunkVersion collectionVersion;
+        ChunkVersion chunkVersion;
+        BSONObj minKey;
+        BSONObj maxKey;
+        std::vector<BSONObj> splitKeys;
+    };
+
+    typedef std::vector<SplitInfo> SplitInfoVector;
+
+    typedef std::vector<MigrateInfo> MigrateInfoVector;
+
+    virtual ~BalancerChunkSelectionPolicy();
+
+    /**
+     * Potentially blocking method, which gives out a set of chunks, which need to be split because
+     * they violate the policy for some reason. The reason is decided by the policy and may include
+     * chunk is too big or chunk straddles a tag range.
+     */
+    virtual StatusWith<SplitInfoVector> selectChunksToSplit(OperationContext* txn) = 0;
+
+    /**
+     * Potentially blocking method, which gives out a set of chunks to be moved. The
+     * aggressiveBalanceHint indicates to the balancing logic that it should lower the threshold for
+     * difference in number of chunks across shards and thus potentially cause more chunks to move.
+     */
+    virtual StatusWith<MigrateInfoVector> selectChunksToMove(OperationContext* txn,
+                                                             bool aggressiveBalanceHint) = 0;
+
+    /**
+     * Requests a single chunk to be relocated to a different shard, if possible. If some error
+     * occurs while trying to determine the best location for the chunk, a failed status is
+     * returned. If the chunk is already at the best shard that it can be, returns boost::none.
+     * Otherwise returns migration information for where the chunk should be moved.
+     */
+    virtual StatusWith<boost::optional<MigrateInfo>> selectSpecificChunkToMove(
+        OperationContext* txn, const ChunkType& chunk) = 0;
+
+    /**
+     * Asks the chunk selection policy to validate that the specified chunk migration is allowed
+     * given the current rules. Returns OK if the migration won't violate any rules or any other
+     * failed status otherwise.
+     */
+    virtual Status checkMoveAllowed(OperationContext* txn,
+                                    const ChunkType& chunk,
+                                    const ShardId& newShardId) = 0;
+
+protected:
+    BalancerChunkSelectionPolicy();
+};
+
+}  // namespace mongo